High surface-area crystalline metal oxides with well connected nanopores are needed for improved performance of catalysts, adsorbents, dye-sensitized solar cells, sensors, lithium-ion batteries etc. Among candidate materials, titania has been extensively used due to its superior physical and chemical properties for photocatalysis, antimicrobial activity, and heavy metal and NOX removal. Developing high surface area bulk porous nanocrystalline rutile with good pore accessibility is crucial for the recovery of hydrogen and sulfur and for further hydrogen energy exploitation.
Currently, commercial titania nanoparticles are manufactured mainly by flame spray pyrolysis. The surface area is as low as about 50 m2/g. High surface area rutile is much less available than anatase. Additionally, the nanoparticles need to be pelletized to reduce the pressure drop of fixed bed reactors or for applications where they need to be recycled from liquid medium for multiple uses. Various surfactants and amphiphilic block copolymers such as pluronic block copolymers have been used to direct the assembly of an initially homogeneous solution into various periodic bicontinuous metal oxide/liquid crystal mesophases. Conventional thermal treatments used to convert the amorphous mesophase into the desired crystalline phase are normally accompanied by rapid crystallite growth and a significant decrease in surface area. Relaxation of the rubbery chains in the pluronic copolymers allows relatively “free” mass transport of the metal oxide species and consequently fast metal oxide growth. Unconfined or less confined epitaxial growth of nanocrystallites distorts or even blocks the pores.
carbon nanospheres, calcium carbonate, polystyrene and silica beads have been thoroughly investigated as sacrificial templates. However, solvent extraction or high-temperature calcination are needed in order to remove these sacrificial templates following the formation of the metal oxides. Further, the embedded isolated nanoparticle sacrificial templates are difficult to remove from the crystalline oxides. Other rigid, high glass transition temperature (Tg) templates such as polyamide and polyethersulfone only result in limited surface area.
Thus, there is a need to develop methods of forming a high surface area high crystallinity well-connected porous metal oxide that is low-cost, non-destructive, and easy to scale-up.